(a) Industrial Field of the Invention
The present invention relates to a magnetic recording/playback apparatus in which a magnetic tape is automatically withdrawn out of a tape cassette having a supply reel and a take-up reel provided therein to record/playback signals by a head, and more particularly, to a tape guide post driving mechanism, a tension servo mechanism and a pinch roller pressing mechanism.
(b) Description of the Prior Art
In a conventional magnetic recording/playback apparatus such as a VTR, a cam groove for a cam gear adapted to turn a tension are is generally formed by utilizing a swing cam. Because this arrangement entails a difficulty in enlarging an angle of turn of the tension arm, it has been required to increase the turn angle through another arm.
A tension post driving mechanism in the prior art will be described below with reference to the drawings.
In FIGS. 31 and 32, a driving force of a loading motor 30 is transmitted to a cam gear 34 through a dual gear comprising gears 31a, 31b, a dual gear comprising gears 32a, 32b, and a dual gear comprising gears 33a, 33b. The cam gear 34 comprises a swing cam in such a manner that as a cam engagement portion 91a of a cam lever 91 moves along a cam groove 34a defined in the cam gear 34 from a position near the center of the cam gear 34 toward the outer periphery, a speed-up gear portion 91b of the cam lever 91 is rotated to turn a tension arm 90 to a large extent so that a tension post 9 is turned to a tape running position show in FIG. 32. When the tension post 9 turns to the tape running position, the cam engagement portion 91a of the cam lever 91 becomes free from the cam groove 34a and, thereafter, the cam lever 91 is balanced by the braking force of a tension band 94 wound around the circumference of a reel stand 99, spring force of a tension spring 92, and tensile force of a magnetic tape wound around the tension post 9, thereby controlling a tape tension.
However, the above conventional arrangement has suffered from such a first problem to be solved by the present invention that the cam lever 91 is needed as a separate member in order to obtain a large angle of turn of the tension arm 90 and, since the cam groove 34a of the cam gear 34 is formed to extend from a position near the center of the cam gear 34 to a position near the outer periphery, it is difficult to form another cam groove for a different purpose, which is problematic in reducing the size, weight and thickness of a magnetic recording/playback apparatus.
Furthermore, various kinds of trials have been recently made for reducing the size, weight and thickness of VTR. A mechanism of pressing a pinch roller in VTRs has also been intensively researched in the past because that mechanism significantly affects the total size of VTR.
A pinch roller pressing mechanism in the prior art will be described below with reference to the drawings. FIGS. 33 to 35 are top plan views showing the pinch roller pressing mechanism in the prior art. Note that to clarify the difference from a mechanism of the present invention (shown in FIGS. 12 to 14), the prior art mechanism is shown as having the same arrangement as the present one except the structure of a cam gear 93.
In the drawings, denoted by the reference numeral 93 is a cam gear having a cam portion 94 formed therein. 60 is a pinch rod which moves in an interlocking relationship with the cam portion 94 of the cam gear 93, and has at one end an elongated hole 95 extending in a direction of length of the pinch rod 60 and a cam follower 96 engaging with the cam portion 94, the elongated hole 95 being fitted over a shaft 97 of the cam gear 93. The other end of the pinch rod 60 is connected through a pin 66 with one end of a first pinch charge arm 65 pivotally supported by a shaft 64 mounted upwardly on a chassis 1. The first pinch charge arm 65 has the other end to which a second pinch charge arm 68 is pivotally supported at its middle portion through a pin 67. A spring 69 is interposed between the one end of the first pinch charge arm 65 and one end of the second pinch charge arm 68. A pin 70 provided at the other end of the second pinch charge arm 68 is fitted into an elongated hole 73 at one end of a pinch arm 72 turnably attached to the chassis 1 through a pin 71, and a pinch roller 12 is attached to the other end of the pinch arm 72 at the same inclination as a capstan 20.
The following is the description concerning an operation in which the pinch roller 12 is press-contacted with the capstan 20 as the cam gear 93 rotates after completing an operation of loading the magnetic tape. As shown in FIG. 33, the cam follower 96 provided on the pinch rod 60 enters a radial region of the cam portion 94 so as to pull the pinch rod 60 in a direction of an arrow d. As a result, the first pinch charge arm 65 is turned in a clockwise direction about the shaft 64 to push the second pinch charge arm 68 in a direction of an arrow g. Then, the pinch arm 72 is turned through the pin 70 in counterclockwise direction about the pin 71 by virtue of the resilient force of the spring 69 is order to press-contact the pinch roller 12 with the capstan 20.
However, the above conventional arrangement has suffered from such a second problem to be solved by the present invention that because the circumferential region of the cam portion 94 is utilized during the loading operation and the radial region of the cam portion 94 is utilized during the operation of pressing the pinch roller 12, it has been necessarily needed to increase the diameter of the cam gear 93 when the distance by which the pinch rod 60 must be moved in the direction of the arrow d to press-contact the pinch roller 12 with the capstan 20 becomes long.
Additionally, the cam gear 93 is required to be rotated through about an angle of about 180.degree. for press-contacting the pinch roller 12 with the capstan 20. Therefore, in an attempt to utilize the cam gear 93 also for some other operation than the operation of pressing the pinch roller, an allowable range of utilization has been limited.
Meanwhile, as one type of braking unit for magnetic recording/playback apparatus, there has been recently used a band brake in a tension serve device.
A first type of tension servo device in the prior art will be described below.
FIGS. 36 and 37 show the first type tension serve device in the prior art. FIG. 36 is a top plan view of the first prior art device and FIG. 37 is a side view of the first prior art device.
In FIG. 37, denoted by 101 is an idler gear provided at such a position as allowing the idler gear 101 to be meshed with a gear portion 103 of an S-reel stand 102. 104 is a felt through which the S-reel stand 102 is press-contacted with the gear portion 103 so as to produce a latch force. 105 is a cylindrical portion formed integrally with the S-reel stand 102. A band 106 is wound around the circumference of the cylindrical portion 105. 107 is a chassis on which a shaft 108 is mounted upwardly with the S-reel stand 102 rotatably fitting over the shaft 108. 109 is a hub attached to the S-reel stand 102 with a tape 110 wound around the hub 109. 111 is a tension arm turnably fitted over a shaft 112. The tension arm 111 has one end at which a tape post 113 is provided, and the other and to which a tension spring 114 and the band 106 are attached. 115, 116 are posts fixed to the chassis 107.
The operation of the tension serve device thus arranged will be explained below. First, when the apparatus is operated in a rewind or review mode, the idler gear 101 is meshed with the gear portion 103 to rotate the S-reel stand 102 counter-clockwise with a certain degree of clutch force. Then, upon entering a playback mode, the idler gear 101 is shifted to mesh with a T-reel stand. The tape 110 now runs in a direction of arrow A and the S-reel stand 102 also rotates clockwise along therewith. The tension arm 111 is urged to turn clockwise by the tensile force of the tension spring 114. Due to this urging force, the band 106 is fastened around the cylindrical portion 105 to apply a braking torque to the S-reel portion 102. Because the tape 110 running in the direction A is wound around the tape post 113, an increase of tape tension creates a moment tending to rotate the tension arm 111 counter-clockwise. This weakens the urging force of the tension spring 114 so that the braking torque on the S-reel stand 102 is lowered to reduce the tape tension. In this way, the tape tension is controlled.
Next, as a second type braking unit for magnetic recording/playback apparatus in the prior art, a soft braking device will be described below.
FIG. 38 is a top plan view of the second type prior art device. Denoted by 140 is a reel stand rotatably fitted over a shaft 141. The reel stand 140 is provided with a cylindrical portion 142. 143 is a brake lever turnably fitted over a shaft 144. The brake lever 143 has at one end a bent portion 143a to which a brake member 145 is fixedly bonded, and at the other end a spring 146 of which the opposite end is fixed to the chassis. The operation of the soft braking device thus arranged will now be explained.
The spring 146 urges the brake lever 143 to turn the same clockwise, whereupon the brake member 145 comes into press-contact with the cylindrical portion 142 for applying a certain degree of braking torque to the reel stand 140.
However, the above first prior art device has suffered from such a third problem to be solved by the present invention that the number of parts used is large and the assembling efficiency is poor. More specifically, though not shown, the first prior art device requires a number of parts. While the band 106 is illustrated as a one piece member, it is actually constituted by sticking a felt to a belt made of phosphor bronze together. Not only is a member for fixing the band 106 to the chassis 107 needed, but also another member for fixing it to the tension arm 111 in a pivotal manner are needed. Additionally, for positioning the tension post, it is typical to insert a band length adjusting mechanism at a point where the band 106 is fixed to the tension arm 111. Thus, the first prior art device requires five or more parts, including the band body. Moreover, when mounting the S-reel stand 102, it must be inserted from above while spreading the band 106 to a sufficient extent, which deteriorates the assembling efficiency.
The above second prior art device has suffered from a disadvantage that when felt or the like is used as the brake member 145, a high degree of braking torque cannot be obtained. Another disadvantage is that when resin or the like is used for the brake member 145 to produce a high degree of braking torque, the brake member 145 as a rigid body is press-contacted with the cylindrical portion 142 through linear contact as shown in FIG. 38 to increase a PV value, hence resulting in reduction in the service life of the brake member 145.